1. Field of the Invention
The present invention relates to a tank transportation system and a production method utilizing the same. More particularly, the present invention relates to a tank transportation system, which comprises suspending a tank from a conveying truck movable On rails under computer control, delivering and/or receiving the tank to and from stations provided at one or both sides of the rails, permitting the tank to carry out predetermined operations at the stations, and moving the tank successively from one of the stations to the next, and to a production method utilizing the same. In particular, the tank transportation system of the present invention is suitable for the production of flowable composites such as paint, which directs toward a multiproduct-small quantity production.
2. Description of the Prior Art
Flowable composites such as paints have been generally produced by using equipment with fixed tanks, pipes and other apparatus and conducting each of the processes such as feeding raw materials, agitation and filling products. In general, the tanks are used while being suspended from and fixed to a second floor, and a first floor is used as a vast space required to set incidental facilities for supplying and receiving the empty cans, and storing products, filling products, delivering and shipping the filled cans, and like purposes. In recent years, multiproduct-small-quantity production is going to prevail in the fields of producing, for example, fine chemicals such as perfumes and various resins such as paints. In order to accommodate to that direction by using the above mentioned fixed-type equipment, the equipment with small tanks equipped with many pipes and valves should become a multi-line type and complicated as a whole, which results in extremely inefficient and less flexible production. Since severe accuracy in avoiding contamination is generally required to guarantee good quality, the tanks, pipes etc. must be washed thoroughly, which requires much labor so that an operator's load becomes larger. Furthermore, the washing is not likely to be complete and the productivity is not high at all. As mentioned above, it is in the present situation that there is much trouble in conducting multiproduct-small-quantity production through the conventional fixed-type equipment.
To improve the fixed-type equipment for the above multiproduct-small-quantity production, Japanese Patent Application Laid-open No. 186572/1985 discloses a method for producing paints which comprises placing a tank for preparing paints on an unmanned tank-carrying vehicle, and permitting the tank to move between stations, each of which corresponds to each of production processes, under computer-Aided remote control.
Japanese Patent Application Laird-open No. 40329/1994 discloses a system adapted to multiproduct small-quantity production, comprising an unmanned tank-carrying vehicle having a lid opening/closing mechanism and another tank-carrying vehicle loaded on the above unmanned tank-carrying vehicle to carry the tank. This production system, moving the tank itself for production, to avoid the aforementioned problems, is considered to be a very rational production method.
Although these methods are considered more suitable for multiproduct-small-quantity production compared with the fixed-type equipment, they need a vast space on the first floor for the unmanned tank-carrying vehicles to travel around, and for the stations and other auxiliary facilities. This has been pointed out as a problem when these methods are introduced, because this tends to offset the following advantage of the aforementioned fixed-type equipment system. The system, in which the tanks are usually suspend from and fixed to the second floor and a filling equipment is placed on the first floor just under the second floor, rationally secures a vast space used for placing incidental facilities to supply, receive, store and fill empty cans, and to send and ship filled cans. Namely, these methods require an separate area to set these incidental facilities an hence need more space for both building area and site than the conventional method, which is not economical and makes stiff the organic relationship with the incidental facilities.
In order to solve the above problems, it has been attempted to provide the filling equipment and other incidental facilities on the first floor and provide a floor space for an unmanned tank-carrying vehicle to travel around, its stations and other auxiliary facilities on the second floor. However, this system completely separates various facilities and working processes on the first floor from those on the second floor by the presence of the floor of the second floor. Furthermore, this system requires the provision of an additional tank-operating floor or the third floor to carry out a prescribed job required for the tank, which causes a problem in view of a working efficiency. Naturally, the above situation is not necessarily limited to the relationship between the first and second floors and the same holds true for the relationship between the floor for the unmanned tank-carrying vehicle to travel on and its upper and lower floors. In the explanations above and below, a limited expression of "the first floor" or "the second floor" is used merely for better understanding, and is not necessarily limited to the literal interpretation.
On the other hand, as a method where an unmanned tank-carrying vehicle does not travel on the floor of the first floor, Japanese Patent Application Laid-open No. 16170/1990 discloses a method for producing paints, which comprises moving a tank consecutively, by means of overhead traveling cranes. In this method, however, although the unmanned tank-carrying vehicle is not required to travel around on the floor of the first floor, stations and other auxiliary facilities still occupy a large area on the floor of the first floor so that the floor is not used effectively. Furthermore, the cranes move in a whole space including a ceiling and must move around avoiding various facilities such as piping to transport the tank, which causes a problem again from the viewpoint of working efficiency. In addition to the above, since the crane is attached to the ceiling together with other belongings, the building structure must be strongly-built, which results in a higher building cost.
As another method to decrease the occupied area of the first floor, Japanese Patent Application Laid-open No. 178755/1991 discloses what is known as a stacker crane method, which comprises moving a tank vertically to carry out each process work. This method also has problems that the first floor is still fully occupied and that working processes are separated from each other over all stages completely due to traveling of the stacker crane. Besides, since transportation capacity of the stacker crane often becomes a bottleneck, this method is not necessarily considered to be rational from the viewpoint of production efficiency and to be suitable for the process for producing paints where a series of consecutive operations are mostly conducted on the same flat plane.
As still another method to decrease the occupied area of the first floor, on which the unmanned tank-carrying vehicle does not travel around, Japanese Patent Application Laid-open No. 23578/1993 discloses a method for transporting a vessel, which comprises preparing a reaction vessel and its detachable heating jacket independently, placing them on a multi-stage type structure, enabling the vessel to move optionally with a stacker crane and/or an unmanned tank-carrying vehicle horizontally on each stage or vertically between the upper and the lower stages. This method has the same problem as in the stacker crane method that working processes are separated from each other completely due to traveling of the stacker crane on all stages. Like the above overhead traveling crane method, this method also has a problem in the working efficiency with respect to the relationship between the traveling of the crane and the position of the vessel.
Among the above mentioned methods, in the methods where the tank is placed on the unmanned tank-carrying vehicle, the center of gravity of the tan is maintained at a high level so that the stability becomes poor and the contents of the tank tend to be shaken to a large extent. In addition, when the tanks with different capacities are used mixedly, it is necessary that the length of the tank-legs be adjusted to keep the tanks at a certain height and to secure workability on the working stage. Then, it becomes almost impossible to transport the tanks stably, because too long legs are required for small-capacity tanks. For the same reason, there are various practical restrictions, such as incapability of optionally setting the height of the working stage.